It's a short book - just over 100 pages and explains the history leading to the current state of English self defence laws. Published in 2006, so fairly up to date. Certainly relevent. It gives the exact legal terminology but follows that up with a summary in everyday language. Case examples are used.

This is a great little book, and its companion - understanding unreasonable force (for force in restraint etc) - is also a good read. The text is a little out of date now, but the core essentials have not changed.